Oil and natural gas that is obtained from oil wells may be stored in an underground oil and natural gas storage facility. There are three general types of underground oil and natural gas storage facilities, including aquifers, depleted oil or gas field reservoirs, and caverns formed in salt or carbonate formations. These underground facilities are characterized primarily by their capacity, i.e., the amount of oil or natural gas that may be held in the facility, and their deliverability, i.e., the rate at which the oil or natural gas within the facility may be withdrawn.
Salt caverns are typically created by drilling a well into a salt formation, e.g., a salt dome or salt bed, and using water to dissolve and extract salt from the salt formation, leaving a large empty space, or cavern, behind. This is known as “salt cavern leaching.” While salt caverns tend to be costly compared to aquifers and reservoirs, they also have very high deliverability, i.e., withdrawal rates, and injection rates. In addition, the walls of a salt cavern have a high degree of strength and resilience to degradation and are essentially impermeable, allowing little oil or natural gas to escape from the facility unless purposefully extracted. Salt cavern storage facilities are usually only about one hundredth of the size of aquifer and reservoir storage facilities, averaging about three hundred to six hundred feet in diameter and two thousand to three thousand feet in height. Accordingly, the capacity of salt caverns may range between around one million barrels to twenty million barrels of oil and natural gas.
In addition to storage considerations, the processing and offloading of the oil and natural gas is also of significant importance. Currently, Floating Production, Storage, Offloading (FPSO) units are often used to meet these demands for offshore environments. FPSOs are floating vessels that are used by the oil industry for the production and storage of oil and natural gas from nearby platforms until the oil and natural gas may be offloaded onto a tanker or ship, or transported through a pipeline. However, the high cost of such surface processing, storage, and offloading equipment limits the ability to efficiently monetize resources, especially in remote or challenging environments, such as Arctic or deepwater developments. For example, in some cases, the majority of the total cost of development may be used for the high capital and operating costs of the facility. Accordingly, a number of research studies have focused on alternate techniques for providing processing and storage facilities.
U.S. Patent Application Publication No. 2009/0013697 by Charles, et al., discloses a method and system for simultaneous underground cavern development and fluid storage. The method and system are directed to the creation of an integrated energy hub that is capable of bringing together different aspects of hydrocarbon and other fluid product movement under controlled conditions. The method and system may be applicable to the reception, storage, processing, collection and transmission downstream of hydrocarbons or other fluid products. The fluid product input to the energy hub may include natural gas and crude oil from a pipeline or a carrier, liquefied natural gas (LNG) from a carrier, compressed natural gas (CNG) from a carrier, and carrier-regassed LNG, as well as other products from a pipeline or a carrier. Storage of the fluid products may be above surface, in salt caverns, or in subterranean formations and cavities. Transmission of the fluid downstream may be carried out by a vessel or other type of carrier, or by means of a pipeline system. In addition, low-temperature fluids may be offloaded and sent to an energy hub surface holding tank, then pumped to energy hub vaporizers and sent to underground storage or distribution.
U.S. Pat. No. 5,129,759 to Bishop discloses an offshore storage facility and terminal. The offshore storage facility and terminal includes a number of underground caverns, an offshore platform that includes a hydrocarbon pipeline extending into each of the caverns, a flow line extending from the platform to single point moorings for connection to off-loading or loading supertankers, a displacing fluid pipeline extending between the salt caverns and a subsea reservoir, and a shore pipeline extending from the platform to shore. As hydrocarbons are off-loaded from the supertanker, a portion of the hydrocarbon stream is directed to the shore pipeline, while the rest is directed to the hydrocarbon pipelines into the underground caverns. As the hydrocarbons flow into the caverns, immiscible fluid is displaced into the displacing fluid pipeline and the reservoir. Subsequently, as hydrocarbons are removed from the underground caverns, the immiscible fluid is pumped from the reservoir into the underground caverns. The underground cavern may thus be used as both surge storage for off-loading supertankers and as long-term storage for hydrocarbons.
International Patent Publication No. WO2000/036270 by Siegfried, et al., discloses a system and method for the transport, storage, and processing of hydrocarbons. The method may be used to form a storage cavern associated with a petroleum well by leaching salt from a salt-bearing formation. The method may also be used for the production of petroleum from a petroleum-bearing formation, which involves connecting a cavern in a salt formation to the petroleum-bearing formation and maintaining the pressure in the cavern at a predetermined pressure to cause a predetermined flow rate of petroleum from the formation into the cavern. Further, the method may be used for the production of petroleum from the petroleum-bearing formation by drilling a single bore hole that connects the surface, the petroleum bearing-formation, and the salt-bearing formation. Thereafter, the salt may be leached from the salt-bearing formation to form a cavern, the petroleum-bearing formation may be used to produce petroleum, and the pressure in the cavern may be maintained at a predetermined level to cause petroleum to flow into the cavern. In addition, a system for producing oil may be created. The system may include a wellbore with an opening that connects a petroleum-bearing formation and a cavern. The system may also include a displacement conduit for the injection or removal of displacement fluid into the cavern.
U.S. Pat. No. 3,438,203 to Lamb, et al., discloses a method for the removal of hydrocarbons from salt caverns. The method involves removing oil and gas hydrocarbons from underground salt caverns by flowing oil and gas into a first cavern containing brine and storing the fluids until the oil, gas, and brine separate. The gas phase may then be removed through a main gas stream to shore, while the oil may be flowed into a second cavern containing brine by utilizing the accumulated pressure within the first cavern. The gas may be diverted from the main gas stream into a third cavern containing brine until the brine is displaced by the gas pressure and flowed into the second cavern, thereby displacing the oil within the second cavern. The oil may then be flowed to a loading zone.
U.S. Pat. No. 6,820,696 to Bergman, et al., discloses a method and system for the production of petroleum using a salt cavern. The method involves drilling a wellbore, wherein the surface is in fluid communication with an oil-bearing and a salt-bearing formation. A salt cavern may be formed by leaching salt from the salt-bearing formation, while the oil-bearing formation may be prepared for production. The pressure in the salt cavern may be maintained below the pressure in the oil-bearing formation in order to allow for the collection of oil in the salt cavern. Periodically, oil may be displaced from the salt cavern to the surface by injecting a fluid into the salt cavern.
However, the techniques above fail to disclose systems or methods for the disposal of waste from a salt cavern without causing a surface footprint. Rather, all of the techniques above rely on the removal of waste products, such as water, brine, or excess hydrocarbons, from the salt cavern to the surface for processing and subsequent disposal. Thus, there is a need for new and improved systems and methods which effectively deal with the problem of waste products, while reducing the cost of operation and the effect on the environment.
Moreover, the techniques above also fail to disclose the full separation of a hydrocarbon stream within an underground formation, such as a salt cavern. Instead, a method for removing a bulk stream of gas or oil from a salt cavern is disclosed. However, the utilized separation methods may not allow for the clean separation of multiple phases within a salt cavern. Therefore, new and improved methods for separating hydrocarbon streams within underground formations are also needed.